The proposed work consists of the development and application of several NMR methods to the delineation of the solution conformation of peptides in general and two cell differentiating pentapeptide fragments in particular. These fragments are the active fragments, respectively, of the thymic hormone thymopoietin which induces selective differentiation of T-lymphocytes, and the ubiquitous polypeptide ubiquitin which induces nonspecifically both T and B cell differentiation. Delineation of the solution conformation of these fragments is an essential prerequisite in understanding the conformation-activity relationships of these fragments. Among the NMR techniques, emphasis will be placed on intramolecular nuclear Overhauser effect experiments, measurement of amide hydrogen exchange rates through transfer of solvent saturation and saturation recovery experiments, and characterization of the conformational flexibility of the pentapeptide fragments through carbon-13 relaxation times.